Jeremy is a snowboarder. one of his best tricks is catching big air, jumping off the ramp while holding on to the snowboard. jeremy did this trick 20 times, the heights (in meters) of which were {18, 23, 15, 16, 15, 17, 22, 16, 19, 11, 24, 14, 12, 16, 20, 18, 14, 13, 21, 11}. what is the median value of jeremy’s big air trick?